Computational Fluid Dynamics (CFD)
What is CFD?
The process of using computers in this way to simulate realistic flows is termed computational fluid dynamics, CFD.
In computer form, the geometry of vehicle designs can be readily defined and modified.
Computational fluid dynamics offers the aerodynamicist a means of exploring a wider range of vehicle shapes than can usually be accomplished, in available time scales, with wind tunnel testing alone.
The type of model used in the simulation is often dependent on the accuracy required, the computer power available and the time scale to perform the analysis.
Role of CFD in Modern Aerodynamic Design
The aerodynamic performance of new designs has traditionally been investigated by using wind tunnel experiments.
In such experiments, a scale model of the vehicle, made to a high degree of accuracy, is held in the working section of the tunnel. Air is passed over the model and the forces and moments on the model are measured.
When performing the experiments, appropriate scaling factors have to be employed, to ensure that the main aerodynamic parameters are close to those encountered in the real, full scale, flow.
Although wind tunnel testing has been a key ingredient in the design of most aircraft in use today, the approach is lengthy and expensive, with a single modern design often utilising thousands of hours of tunnel testing time.
The building of models is costly, and minor changes in geometrical shape often require the construction of a new model. The tunnels themselves are expensive to build and operate and they have limited applicability for a full range of flight conditions.
Significant developments have been made in an alternative testing procedure, based upon the use of computer simulation methods for the analysis of the aerodynamic performance of vehicle designs.
As wind tunnel costs have increased, the cost of high performance computers has decreased, and computers capable of performing certain complex flow simulations are now widely available.
Swansea University and CFD
Swansea University has led the development of state of the art techniques for the simulation of complex aerodynamic flows. The procedure has been fully automated and highly tuned for the use in the aerospace design cycle. These procedures form the basis of the original FLITE system, extensions of which are now in production use in AIRBUS, BAE SYSTEMS and Rolls Royce.